[composite] Grace notes are not handled properly in the analysis spines

[craigsapp]

Example:

**kern	**kern
*part1	*part1
*staff2	*staff1
*I"Piano	*I"Piano
*grp:A	*grp:B
*clefF4	*clefG2
*M4/4	*M4/4
8qD	.
4C	2cc
4C	.
4C	2cc
4c	.
=	=
*-	*-
!!!system-decoration: {(p1)}
!!!filter: composite -ceg | colorgroups

The grace note in the group A notes is not transferred to the group A analysis spine, and the coincidence spine has an unwanted rest.

Adding a grace note to the other group:

No the coincidence has a grace note, but no visual duration, and the group analysis spines do not have grace notes as well as the composite.

**kern	**kern
*part1	*part1
*staff2	*staff1
*I"Piano	*I"Piano
*grp:A	*grp:B
*clefF4	*clefG2
*M4/4	*M4/4
8qD	8qdd
4C	2cc
4C	.
4C	2cc
4c	.
=	=
*-	*-
!!!system-decoration: {(p1)}
!!!filter: composite -ceg | colorgroups